Mtlo g



(No Model.)

M. G. KELLOGG.

MULTIPLE SWITGHBOARD.

Patented Oct, 26

f .la

NiTnn STATES PATENT Prion.

MIIJO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO TIIE KELLOGGSVITCIIBOARD AND SUIPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,306, dated October26, 1897. Application filed February l, 1888. Serial No. 262,664. (Nomodel.)-

To @ZZ whom t may concern:

Be it known that I, MILO G. KELLOGG, of Chicago, Illinois, have inventedcertain new and useful Improvements in Multiple Switchboards forTelephone-Exchanges, of which the following is a full, clear, concise,and eX- act description, reference being had to the accompanyingdrawings, forming a part of this specification.

My invention relates to a telephone exchange system in which parts ofthe subscribers lines are single or ground circuit lines and part of thelines are metallic-circuit lines;

and it consists of apparatus and a system of testing such lines todetermine at one board whether a line is in use at another board, whichrequires of the operator practically the same operations, whether theline tested be a single ground-circuit line or a metallic-circuit line.

In the drawings illustrating my invention, Figures 1a and lb representsections of two multiple switchboards of the exchange to which the samelines are connected. Fig. 2 shows a complete diagram of the boards withall the central-oliice apparatus, circuits, and connections necessary tooperate them according to my invention. Fig. 3 shows a diagram of thesubscribers-station apparatus adapted for use on the metallic-circuitlines of the system.

In Fig. 2, A is a sectional view of the switchboard shown in Fig. l, andA is a sectional View of the switchboard shown in Fig. lb, each asindicated by the line CZ e. I place as many boards in the central oliieeas are found necessary or desirable in order to properly answer thecalls and make the necessary counections. On each board is a suitableswitch for each line. Each switch has a contactspring which normallybears on an insulated In Fig. 2, g g represent the springs of thedierent switches, ZZ 7i the contact-points on.

are used for metallic-circuit lines, should be so placed that at-est-plug or other switch testing device may be readilyv applied tothem. For the single-circuit lines I use test contact-pieces separatefrom the line-switch contact-points and holes, but which may be adjacentto the holes. I use one such test contact-piece for each line on eachboard. These pieces are marked t' i. l

I use a loop-switch plug with' double liexible cord for each line on theboard where its calls are to be answered. These plugs are marked D D',the construction of the plugs being the same whether they are forsinglecircuit or metallic-circuit lines, but the connections to theplugs being different for the diiiferent kinds of lines.

In Fig. E2, D is for a single-circuit line, and D is for ametallic-circuit line.

For each loop-switch plug at the board where it is located I provide aswitching device adapted to receive the plug and into which the plug isnormally placed and'which normally connects one'of the contact-pieces ofthe plug with the ground wire or connection of the lines, as shown andas will hereinafter be described.

r r are the switching devices for the two lines shown, one device oneach board.

Z Z are the holes in which the plugs are normally placed, and g g' arecontact-springs of the devices with which one of the contactpieces ofthe plugs connects when the plugs are inserted. l

fm m are the two insulated contact-pieces of a plug, and n is the rubberinsulation of the plug.

IOO

All the springs g g of the several switch-v ing devices connect todaground ',wire'orconnection in which is a battery B', as shown.

For each line there is a looping-in switch (marked T) connected in theline-circuit as shown and by which the operator attending theline-mayatwill loopreither her telephone or calling-generator in its'circuit.Thelooping-in switch of a line is located at the board where thelooping-in' plug of the li-ne is `located and where the calls of4 theline are to be attended to. yIt should be convenientlymounted .andplaced sol that theoperator can readily ma'ke the connections.

In the subscribers-station apparatus for metallic-circuit lines, shownin Fig. 3, l is the telephonefswitch'. 2 is the calling-generator.

3 is-.th'efsgnal-receiving bell, ,and 4L isthe.

G is'the ground condescribed."` v

The; generator has an automaticfdevice:

(shown: in* the, drawings) by, which?, when the. crank-,isA-not inmotion, .the wireof thearma.-Y tureis-shunted `and the.A line is.disconnected from the ground lat the subscribers: station, andfwhen:the generator isfturned or'operated the, shunt is automatically removedtand :thel

line is-connected to the. ground. Theauto.. matie devicershow-n isa-moditication,of a.- for-nr, very. generally used, the in odication.

being-substantially inthe arrangementgof the.:

contact-points. It contains aV-'shaped'at-z tachmenttothe hub of thedrivin g-wheehapin;

in the shaft which` engages inthejv :shaped arrangement, and; a;spring.- wh-ich presses against the-wheel and-brings the pin`normally-in the: centerofl the V.;arrangement.`

T'he-,contact-points are substantially as shown and: as will producerthe switchingoperations described above.

w and ware; calling-annunciators, rone for eachline shown, and eachlocated in the-cir cuit offits, 4lineat the board :whereitscalls are tobe answered; Two lines arel shown, one a metallic-circuit line andmarked line No. l :and the otherasingle-ci-rcuit line and marked-lineNo.2. The two sides orbranches of :thermetallic-circuit line are markedwirea and ,wire b.'

Thefcircuit of thesingle-circut line is as follows l:. from. the.subscribers` ground 'throughi his station apparatus, (which maybe of:the

usual style for such'lines,) through the pairs of contact-points,successively, of its switches;

onfthe. several boards, goingin each case to thefspr-ing .Iirst, thencethrough `its` line-annunciator'to one of the conductors ofits dou.-

blef-cord and thence to vthecontact-piece m ofl its double plug, and,when the plug is inserted inftoV its'y switchingV device, to '.theyground through the contact-spring g and the battery B. The looping-inswitch is in the circuit of the line, as shown, before it is connectedto These partsrnay be the usual forms:

it is`connected to the plug.

the plug. The other contact-piece m of the plugot a singlecircuit'` lineis connected through the other conductor of its cord to the ground or tothe common ground-wire, but the battery Bf should not be in itsgroundcircuit. All the contact-pieces j y of the jswitches ofasingle-circuit line should be connected together and to the ground or tothe common ground wire, but the battery B' `should not be in theirground-circuit. All the test contact-pieces i t' of a single-circuitline should be connected together and to the line,

the connection to the line being between its "switches and thesubscribers station. The idrawings-show the connections of asinglecircuit line and its switch parts and apparatus as describedabove,

The circuit of` ametallic-circuit line is as ufollows: Onel sideor'branchoffthe line, ,say wirea, is connected with all thecontact-pieces j j ofits'switches on the several boards-and also to thecontact-piece mI ofV its loop-plug through -oneof they conductors of:the double cord.l The other side or branch of the lineV lpassessuccessively through ,thepairsfof contact-points g.. h of its switcheson `the several boards, going in each case to the springrst,thence,through,itS-annunciator to the other conductor of the cord, andtothe contact-` zpiece m of its doubleplug, and, when the plug`,is-.inserted into its switching device, through the contact-ispringgand the lbattery B to lground. The looping-in switch is-in the ciricuitof :th-is side'. of the line, as-shown, before Thetwo sides of fthe lineunite at the subscribers station, and

thei subscribers-station apparatus-.is Y so connected into thecircuit-that when the generator ,is operated' the ground connectionthere- Aby established vis between thewire of thearmature` andthecontact-pieces j 7` ofthe iswitches.v In each case in the switching when"a plug is taken from its normal position in its sswitchingvdevice andplaced in a line-switch it is ,so placed :in thei switch that thecontactpiece of the plug marked m) makes connection with thespring-lever g ot the switch. To insure this, the piecefm may besuitably marked. The metallic-circuit lines are normally grounded onlyat thecentral office and as;indicated., Y

t The switching between thevarious'lines of theeXchan-ge is as follows:lVhen an opera- 'tory receives a `call from a metallic-circuitlinelassig'nedto her boardto be answered, fsheiinds out by testing, aswill hereinafter be described., Whether the line called for is in use.-lf` it is-not in use, she takes the plug lof "the line: calling from itsnormal position 'and places it, as indicated,in the switch at her boardof the linewanted. By so doing she removes vthe ground connection,through the 4battery B', Vfrom both lines. If the line wanted is-alsoa/metallic-circuit line, the two lines are connected together in anungrounded metallic circuit. The annunciator and the looping-in switchof the line which called is IOO IIO

in that circuit, and the annunciator and looping-in switch of the otherline is not in that circuit. If the line wanted is a single-circuitline, the two lines are connected together into one circuit with theannunciator and looping-in switch of the calling-line in the circuit andthe annunciator and switch of the other line not in the circuit. Thecombined circuit is thus: from the ground of the single-circuit line atthe subscribers station through the line to the contact-piece of theloop-plug which is in connection with the spring-lever of the switchused, thence through the metallic-circuit line to the othercontact-piece of the plug, and through it to the contact-piece j of theswitch used, and thence to ground. lVhen an operator receives a call ona single-circuit line assigned to her board to be answered, she findsout by testing whether the line called for is in use at another board.If it is not in use, she takes the plug of the line calling from itsnormal position in its switching device and places it, as indicated, inthe switch at her board of the line wanted. By so doing she removes theground connection, through the battery B', from both lines. lf the linewanted is a metallic-circuit line, the two lines are connected togetherwith the looping-in switch and annunciator of the calling-line in theircircuit and the others not in the circuit. The combined circuit is thus:from the ground of the single-circuit line at the subscribers stationthrough the line to the contact-piece m of its loop-plug, thence throughthe spring-lever of the switch used and the metallic-circuit line to thecontact-piece?l of the switch, thence to the contact-piece fnt' of theplug and to the ground through its leXible conductor. It the line wantedis a single-circuit line, the lines are also connected together in acircuit in which are the annunciator and looping-in switch of thecallingline only. The combined circuit is from the ground at thesubscribers station of the callingline, through the line to thecontact-piece on, of its plug, thence to the spring-lever of the switch,and through the line wanted to its ground at the subscribers station.The other contact-piece of the plug is in this case connected with thecontact-piece j of the switch. Both are connected with the ground only,an d the operation ofthe system is not affected thereby.

For each operator at her board I provide a test receiving instrument,grounded at one side or connected to the ground connection, (but thegroundcircuit of the instrument must not be through the test-battery B,)said instrument being connected on its other side to a test-plug with aflexible cord or other suitable test arrangement, by which the' operator may connect her test receiving instrument on that side at will toany of the contact-pieces jj at her board of the metallic-circuit linesand to any of the contact-pieces t at her board of the single-circuitlines. The

test receiving instruments are marked S and the test-plugs are marked T.In each casein the drawings, G represents the ground connection.

The test is applied for any line to determine whether or not it is inuse by connecting the vflexible cord, plug, and switching device of theline to the ground through the battery B, and her instrument willrespond to the battery. It' the line is switched, either by itsswitch-plug being withdrawn from its normal position or by a plug beinginserted in any of its line-switches, this test-circuit is interrupted,and as no battery will then pass through the instrument it will notrespond. The test-circuit 'of a single-circuit line when not in use -isfrom the ground of the test instrument through the instrument to thecontact-piece fr' of the line, thence through the pairs of contactpointsof the line-switches and the flexible cord, plug, and switchingdcvice'ot` the line to the ground through the bat-- tery B, and herinstrument will respond to the battery. It the line is switched, eitherby the ,switch-plug being withdrawn from its normal position or by aplug being inserted in any of its line-switches, this test-circuit isinterrupt-ed, and as no current will pass to the instrument it will notrespond. In either case the operator may tell whether a line is in useor not by the fact that her test receiving instrument does not or doesrespond.

It will be seen from the description of the system as above describedthat the operators can make all the necessary connections and testingfor a telephone system with combined single and metallic circuit lines,and that the operations they go through with for each connection are thesaine whichever kind of lines are switched. The confusion which wouldresult from having two systems of testing and switching for the twokinds of lines is avoided. This result is obtained by the combination ofapparatus I have shown.

The system herein described varies from that of my Reissue Patent No.11,388, being a reissue of my Patent N o. 393,508 for which applicationwas filled November 14, 1887, as far as the same relate to the testsystem for metalliccircuit lines, especially in the fact that in thesystem of said patent the test-battery is in the test-wire from groundto the test-plug, in which is also the test receiving instrument, and istherefore always in the circuit with the test receiving instrument,whereas in the system of this application the test-battery is the normalground connection of the lines at the central office from which thelines are disconnected when they are lOO IIO

. vantagesy over the system ofl said patent;

switched for conversation, and the battcryis therefor-ein circuit withithetest creceiving in-` strumenten-ly while-the test of a line-is beingmade and when the line is not then switched for conversation.Thiskdi'tterence in therelative position oy theJtest-battery to thetestreceiving instruments and the circuits Vpro-- duces a system which invarious waysl hasad- In the system of= thisappl-ication. the line willnot test free?? or unswitched,when already switched for use from-anycurrent passing from the test-batterythroughthe testreceiving-instrument whenthetest of a line is made, from any4 accidentalground or escape'which mayexist on.thefline,becausethe battery in thisfsystem Y is--then entirely. out of circuit withgtthe line. It is,moreover, well known] that Atelephone-lines have in practice a lstaticcapacity, varyingA in. :amount with their character. and general 1construction, and that on account ofl f such .static capacitywhen =agrounded Itest-.wiref containing a test lreceiving instrumentand batteryis connected to such aline the -line becomescharged :froml the battery,and during-the period' of` charg ing currentpasses vthro-ugh the testlreceiving instrument, and precautions :must be ob-` servedthat a.falsetest isinotf thereby indi# cated. lWith the test-battery relatedto the test receiving instruments and located as de scribed invthisapplication there can be no static charge of the, line from: the batterythrough the test receivingl instrumentwhen the `test is made,and'therefore no liability from this source of false test-signals.

I claim4 as .my invention and desire to securel by Letters Patent- 1.Ina telephone-exchange system, multiple switchboards,a single-circuitlin egrounded at its outer'end, a switch on eachA of'said boards .forsaid line, each switch containing a pair of contact pointsor piecesnormally in contactv and ay third contact-piece normally"`insulated'from the rest"(except by the-line connections), the linepassing successively throughysaid lpairs of contact-piecesv of itsswitches and thence normally or while thel line is` not switched forconversation to a ground wire or connection and' a battery in saidground wire or connection, said normallyinsulated contact-piecesof .itsswitches being also` connected tov ground, but not through a battery,and .a nloop-switch1 plug, the two contact-pieces of Vwhich areconnected to the two l sidesor branches ofa metallic-circuit line,

' one of the switch-holes and'when inserted to said plugbeing adapted tobe inserted into disconnect the pairof contact-points which arenormallyin contact and connect the two contact-pieces ofthe plug, one with saidnormally-insulated contact-piece -of the switch and the otherwith thatcontact-piece of thebolt being apart from thel switch-hole oftheline andconnected to the line, and'test re-V ceiving instruments, one ateachboard, eachl tes-t receiving instrument being grounded on @one side butnot through a battery and-con nected on itsother side to a test-plug orother test device adapted ,to bebrought into con- :nectionwiththetest-bolt at'its board, sub-` stantially asset forth. l

" '2. Inatelephone-exchange system, multiplev switchboards, single and4metallic circuit lines connected to said boards, a ground connectionfor said lines fat thecentral office,- a battery in said groundconnection, one branch of each of fsaid metallic-circuit lines and saidsingle-circuit lines being normally or while they are not switched forconversation connected to said ground connection, the other branch. of`each of said metallic-circuitlines normally and while the subscribersgenerator is not operated ungrounded at the subscrib ersv stations, andswitching devices at each board for each ofthe lines to disconnect thelines from the ground when they are switched for con-versation, incombination with test receiving instruments,- one at eachv board, eachinstrument being groundedon one side (but not through a battery) andconnected on its other side toa switch testing plug or de-` vice adaptedat the Willof the operator to connect the instrument to anysingle-circuit line and to the normally open branch of 'anymetallic-circuit line at her board, substantially as set forth.

3. In a telephone-exchange system, a loopswitch plug, the twoinsulatedcontact-'pieces of'whichI are connected to the two sides or branches,respectively, of a metallic-circuit line, in combination with aspring-jack-switch for a sin gle or ground circuit line, said switchhavingl two contact-pieces normally in contact and a thirdcontact-piece, normally insulated from the rest (except by thecircuitconnections), one of said contact-pieces which arev normally incontact being connected with theline and the other being normally orwhileconnected to the ground, butnot through a battery, said plug beingadapted-to be inserted into said switch and when inserted to disconnectthel two contact-pieces of the switch which'are normally in contact andconnect the two contact-pieces of the plug, respectively, with thatcontact-piece of the switch'which is connected to the line and with saidthird contact-piece of the switch, substantially asset forth.

4.' In a telephone exchange system, a spring-jack switch con tainingvacontact-piece connected to the line, a contact-piece normally or whilethe line is not switched for conversation in connection with said othercontact-piece and grounded, a battery in the ground connection, and athird contact-piece insulated from the rest (except by the circuitconnections) and grounded, but not through the battery in combinationwith a double or loop plug adapted to be inserted into said switch andwhen inserted to disconnect said contact-pieces which are normally incontact and connect one of the contact-pieces of the plug with saidfirst-mentioned contact-piece of the switch and the other contact-pieceof the plug with said third contact-piece of the switch, substantiallyas set forth.

5. In a telephone-exchange system, multiple switchboards, atelephone-line, a springjack switch on each board for said line, eachswitch containing a pair of contact-points which are normally in contact(and a third contact-piece which is placed along the surface of saidswitch-hole), said line normally or while the line is not switched forconversation passing successively through said pairs of contact-piecesof its switches and thence to a ground wire or connection, a battery insaid ground wire or connection (and said third contact-piece beingconnected to ground but not through a battery), in combination withtest-bolts, one for the line on each board, each bolt being placed apartfrom the switch-hole ofx the line and connected to'nthe line, and testreceiving instruments, one at each board each grounded on one side andconnected on its other side to a test plug or device, adapted, at thewill of the operator to be brought into connection with the test-bolt atits board, substantially as set forth.

6. In a telephone-exchange system, multiple switchboards, atelephone-line, a springjack switch on each board for said line, eachswitch containing a pair of contact-points which are normally incontact, said line normally or while the line is not switched forconversation passing successively through said pairs of contact-piecesof its switches and to aground wire or connection, and a battery in saidground wire or connection, in combination with test-bolts, one for theline on each board, each bolt being placed apart from the switch-hole ofthe line and connected to the line, and test receivinginstruments, oneat each board, each grounded on one side but not through a battery andconnected on its other side to a test plug or device adapted, at thewill of the operator, to be brought into connection with the test-boltat its board, substantially as set forth.

7. In atelephoneexchange system,a switchboard, a telephone-line, aswitch on said board for the line, containing a pair of contactpiecesnormally in'contact and a third contactpiece normally insulated from therest (except through the circuit connections), one of j saidcontact-pieces which are normally in contact being connected to the lineand the other normally or while the line is not switched forconversation connected to a ground `wire or connection, a battery insaid ground wire Or connection, andsaid third contact-piece being alsoconnected to the ground, but not through a battery, said switch beingadapted to receive a switch-plug and said plug when inserted adapted toconnect said third contact-piece with one end of another line, incombination'with an insulated test-bolt connected to the line and a testreceiving instrument grounded on one side and connected on its otherside to a test plug or device adapted at the will of the operator to bebrought into connection with said test-bolt.

8. In a telephone-exchange system,a metallic, circuit-line, the twosides or branches of which terminate in the two contact-pieces,respectively, of a loop-switch plug, a switching device for said plug inwhich it is normally placedsaid switching device having a contact-piecewhich is connected to the ground through a battery, said plug having oneof its contact-pieces in connection with said contact-piece of theswitching device when in its normal position and adapted to be removedfrom said normal position and placed in the switch of another line, incombination with a test receiving instrument grounded on one side butnot through a battery and connected on its other side to a test plug ordevice adapted, at the will of the operator, to be brought Vintoconnection with said line, substantially as set forth.

9; In a telephone-exchange systein,two mey tallic-circuit lines,incombination with double or loop plugs, one for each line, in the twocontact-pieces of which the two sides or branches of the line,respectively, terminate, switches, one for each line, each switch havingtwo contact-points, normally in contact, in the circuit of one of thesides or branches of its line, a switching device for each plug, inwhich the plug is normally placed, each switching dcvice having acontact-piece which, when the plug is inserted, is in connection withthat side or branch of the line in which are said contact-points of itsswitch and which contact-piece is connected to the ground through abattery, said plugs being each adapted to be Withdrawn from their normalposition and placed in the switch of the other line and therebydisconnect the lines from their ground connection and connecting themtogether, in combination with a test receiving instrument grounded onone side but not through a battery and connected on its other side to aswitch testing plug or device adapted to be brought into connection witheither line, substantially as set forth.

10. In a telephone-exchange system, metallic-circ uit lines normallygrounded at the cenroo IIO

tral office and there only, line-switching devices at the centraloffice, one for each line, each switching device containing threecontact-pieces, two of which are normally in contact, and one of saidpieces which are normally in contact being connected to one sideorbranch of its line, and the third contactpiece being connected to theother side or branch of its line, double or loop plugs with doubleflexible cords,'one for each line, the I two conductors of each cordbeing Arespectively attached to the two sides or branches of its line,and the other ends of the conductors being attached to the twocontact-pieces of their plu g,respectively,and ground switchingdevices,.one foreach plug in which the plug is normally placed, each ofsaid switching'dcvices having a contact-piece which is connected to theground through a battery, and when its plug is in its normal positiontherein,'connecting said contact-piece with that contact-piece of theplug which is connected to the same side or branch of the line as itssaid pairs of contact-points are in, said plugs being adapted to bewithdrawn from their normal positions and placed in the switch ofanother line, and when so placed to disconnect the two lines from theirground connection through the battery and connect them together, incombination with a test receiving instrument grounded on one side butnot througha battery, and connected on its other side to a switchtesting plug or device adapted, at the will of the operator, to be.brought into connection with either of said third contact-.pieces of theswitches, substantially as set forth.

1l. Ina telephone-exchange system, metallic-circuit lines normally`grounded at the central ofiice and there only, multiple switchboardsfor said lines, line-switching devices for said lines, 'one for eachline on each board, each switch containing three contact-pieces, two ofwhich are normally in contact, the contact-pieces of the switches whichare normally in contact being in the circuit of one side or branch oftheir line and the other contactpieces of the switch being connected tothe other side or branch of the line, double or loop plugs with doubleflexible cords, one for each line, the plugs beingdistributed among theseveral boards, the two conductors of each cord being attached to thetwo contact-pieces of its plug, respectively, and thel other` ends ofthe conductors being attached to, Ithe two sides or branches of theirline, respectively, and `ground switchingdevices at the several boardsfor said plugs, each ground switching device having a contact-piecewhich is connected to the ground through a battery, said l. plugs beingnormally placed in their ground switching device and when yso placedgrounding that side of their line in which are said pairs ofcontact-points, through the battery, each of said plugs being adapted tobe withdrawn from its normal position and placed in the switch ofanother line and thereby disconnect the two lines from their groundconnection through the battery and connect them together, in combinationwith test receiving instruments, one at each board, each instrumentbeing grounded on one side, *but` not through a battery and connected onits other side to a switch testing plug or device,l adapted, at the willof the operatorgto be brought into connection with any of said thirdcontactpieces of the switches at its board, substantially as set forth.

12. 'In a telephoneexchange system, the combination of ametallic-circuit line, a switch-plug for the line, a switching deviceinto which the plug is normally placed and on which'it operates, aground wire or connection with which one side or branch of the line isnormally in connection, a battery in said ground wire or connection andcontacts by which such normal connection of the line with the groundwire or connection is automatically broken when the plug is withdrawnfrom its normal position in the switching device, substantially as setforth.

13. In a telephone-exchange system, the combination of a telephone-line,a switchplug for the line, a .switching device into which the plug isnormally placed and on which it operates, a ground wire or connectionwith which the line is normally in connection, a battery in said groundwire or connection and contacts by which such normal connection of theline with the ground wire or connection is automatically broken when theplug is withdrawn from its normal position in the switching device,substantiallyas set forth. Y

14. In a telephone-,exchange system, a metallic-circuit line, aswitch-plug for lthe line, a switching device into which the-plug isnormally placed and on which it operates, a ground wire or connectionvwith which one side or branch of the line is normally in connection, abattery in said ground wire or connection and contacts by which suchnormal connection of the line with the ground wire or connection isautomatically broken when the plug is withdrawn from its normal positionin the switching device, in combination with a test receiving instrumentgrounded on one side and connected on its other side to a plug ordev-ice adapted to be brought for testing into connection with the line,substantially as set forth.

15. In a telephone-exchange system, a telephone-line, a switch-plug forthe line, a switching device into which the plug is normally placed andon which it operates, a ground Wir-e or connection with which the lineis normally in connection, ay battery in said ground wire or connectionand contacts by which such normal connection of the line with theg-round wire orconnection is automatically broken when the plug iswithdrawn from its normal position in the switching device, incombination with a test receiving instrument grounded on one side andconnected on'its other side to a plug or device adapted to be broughtfor testing into connection with the line, substantially as set forth.

16. In a telephone-exchange system, the combination of ametallic-circuit line, a switch-plug for the line having a contact-piecewith which one side of the line is normally connected, a switchingdevice into which the plug is normally placed, a contact-piece in IOOIIO

said switching device with which said contact-piece of the plug comes'incontact when the plug is inserted into the switching device, a circuitwire or connection connected on one side to said contact-piece of theswitching device and grounded on its other side, and a test-battery insaid cireuit-wire, substantially as set forth.

17. In a telephone-exchange system, the combination of a telephone-line,a switchplug for the line having a contact-piece with which the line isnormallyV connected, a switching device into which the plug is normallyplaced, a contact-piece in said switching device with which saidcontact-piece of the plug comes in contact when the plug is insertedinto the switching device, a circuit wire or connection connected on oneside to said contactpiece of the switching device and grounded on itsother side, and a testbattery in said circuit-wire, substantially as setforth.

18. In a telephone-exchange system, a metallic-circuit line, the twosides or branches of which are normally open to each other at thecentral office, a ground connection through which one side or branch ofthe line is grounded there, and a battery in said ground connection, incombination with a switch for the line adapted to receive theswitch-plugs of other lines, a pair of switch contacts normally closedbut open while a plugis in the switch, a switch-plug for the line, aplug switching device in which the plug is normally placed, and a pairof contracts which are closed while the plug is in the switching deviceand opened by the withdrawal of the plug from the device, said branch ofthe line which is normally grounded passing through said pair ofswitch-contacts and thence through said other pair of contacts toground, substantially as set forth.

19. In a telephone-exchange system, a metallic-circuit line, the twosides or branches of which are normally open to each other at thecentral office,a ground connection through which one side orbranch ofthe line is grounded there, and a battery in said ground connection, incombination with a switch for the line adapted to receive theswitch-plugs of otherlines, a pair of switch-contacts normally closedbut open while a plugis in the switch, a switch-plug for the line, aplug switching device in which the plug is normally placed, a pair ofcontacts which are closed while the plug is in the switching device andopened by the withdrawal of the plug from the device, said branch of theline which is normally grounded passing through said pairofswitchcontacts and thence through said other pair of contacts toground, and a test receiving instrument grounded on one side andconnected on its other side to a plug or device adapted to be broughtfor testing into connection with the other side or branch of the line,substantially as set forth.

20. In a telephone-exchange system, a metallic-circuit line the twosides or branches of which are normally open to each other at thecentral office, a ground connection through which one side or branch ofwhich is normally grounded there7 and a battery in said groundconnection, in combination with switches for the line, one on each ofthe multiple switchboards, each switch being adapted to receive theswitclrplugs of the other lines located at its board, a pair of contactsfor each switch which are normally closed but opened while a plug is inthe switch, a switch-plug for the line, a plug switching device in whichthe plug is normally placed and a pair of contacts which are closedwhile the plug is in the switching device and opened by the withdrawalof the plug from the device, said branch of the line which is normallygrounded passing successively through said pairs of its switch-contactpoints, and thence through the other pair of contacts to ground,substantially as set forth.

21. In a telephone-exchange system, a metallic-circuit line the twosides or branches of which are normally open to each other at thecentral ofce, a ground connection through which one side or branch ofwhich is normally grounded there, and a battery in said groundconnection in combination with switches for the line, one on each of themultiple switchboards, each switch being adapted to receive theswitch-plugs of the other lines located at its board, a pair of contactsfor each switch which are normally closed but opened while a plug is inthe switch, a switchplug for the line, a plug switch device in which theplug is normally placed, a pair of contacts which are closed while theplug is in the switching device and opened by the withdrawal of the plugfrom the device, said4 branch of the line which is normally-groundedpassing successively through said pairs of its switch-contact points,and thence through IOO the other pair of' contacts to ground, and a ttest receiving instrument grounded on one side and connected on itsother side to a plug or device adapted to be brought for testing intoconnection with the other side or branch of the line, substantially asset forth.

MILO G. KELLOGVG.4 Vitnesses MILTON HEAD, CALVIN DE WOLF.

